The present invention relates generally to a magnetic disk drive and, more particularly, to an adjustment of a rotational balance after assembly of a disk assembly.
In recent years, efforts are being made to achieve a higher rotating speed of the disk in order to meet the need for an improved access performance in a 2.5-inch disk drive. Self-oscillation is involved here of the magnetic disk, arising from imbalance of a spindle motor itself or imbalance caused by eccentricity of different members of the magnetic disk after assembly. The self-oscillation tends to increase in proportion to the rotating speed of the disk to the second power. The effort made to increase the disk rotating speed in the 2.5-inch disk drive could make the self-oscillation more pronounced, resulting in inconveniences such as impaired quietness or the like.
Conventionally, effort has been made to reduce the self-oscillation by improving accuracy in aligning centers of gravity when the magnetic disk or clamps for holding the magnetic disk are assembled onto a hub (motor hub) of the spindle motor.
In a large-sized disk drive, approaches are taken to reduce the self-oscillation by placing a screw or driving a plastic pin as a counterweight at a position for canceling the imbalance. One patent reference is Japanese Patent Laid-open No. 2000-184678.